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United States Patent |
6,205,219
|
Hollenbach
,   et al.
|
March 20, 2001
|
Call related information reception using sigma/delta modulation
Abstract
A method and apparatus to receive and demodulate call related information,
e.g., Caller ID information, in an audio codec placed on the line side and
powered by current drawn from the telephone line. The audio codec includes
a 1.sup.st order .SIGMA./.DELTA. A/D converter to digitize the signal from
the telephone line with .SIGMA./.DELTA. modulation. The 1.sup.st order
.SIGMA./.DELTA. A/D converter may be a scaleable component capable of
alternative operation in a 2.sup.nd order. The .SIGMA./.DELTA. encoded
digitized signal is digitally processed by a DSP including an amplifier
module, a digital filter, a limit/slice module, and an FSK decoder to
receive and output the call related information. Placement of the audio
codec on the line side and the scaleable .SIGMA./.DELTA. A/D converter
provides significantly reduced power requirements for the audio codec,
thus allowing operation from power derived from the telephone line. In
another embodiment, to further reduce power consumption of the audio
codec, the 1.sup.st order .SIGMA./.DELTA. A/D converter is sampled at a
slower rate than is conventional, e.g., by first dividing or otherwise
providing a slower sampling clock.
Inventors:
|
Hollenbach; Keith Eugene (Kutztown, PA);
Laturell; Donald Raymond (Upper Macungie, PA);
Witmer; Steven Brooke (Sinking Spring, PA)
|
Assignee:
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Lucent Technologies, Inc. (Murray Hill, NJ)
|
Appl. No.:
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028478 |
Filed:
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February 24, 1998 |
Current U.S. Class: |
379/413; 379/93.36 |
Intern'l Class: |
H04M 019/00 |
Field of Search: |
379/93.01,93.06,93.03,93.15,93.28,93.36,413
375/247,334
|
References Cited
U.S. Patent Documents
4851841 | Jul., 1989 | Sooch | 341/143.
|
4852152 | Jul., 1989 | Honick | 379/97.
|
5086454 | Feb., 1992 | Hirzel | 379/98.
|
5189419 | Feb., 1993 | Lyden | 341/143.
|
5369687 | Nov., 1994 | Farkas | 379/98.
|
5875235 | Feb., 1999 | Mohajeri | 379/93.
|
5940019 | Aug., 1999 | Maejima | 341/143.
|
Other References
Boser et al.; Quantization Error Spectrum of Sigma-delta Modulators; ISCAS
1988, pp. 2331-2334, 1988.*
Comino et al.; A First-Order Current-Steering Sigma-Delta Modulator; IEEE
1991; pp. 176-183, 1991.*
Yu et al.; Adaptive quantisation for one-bit sigma-delta modulation; IEEE
Preceedings-G, vol. 139, No. 1, pp. 39-44, Feb. 1992.*
Jansson; A High-Resolution, Compact, and Low-Power ADC Suitable for Array
Implimentation in Standard CMOS; IEEE 1995; pp. 904-912, 1995.*
Kiriaki; A 0.25 mW Sigma-Delta Modulator for Voice-band Applications; 1995
Symposium on VLSI Circuits Digest of Technical Papers; pp. 35-36, 1995.*
Analog Devices et al., "Audio Codec '97; Component Specification; Revision
1.03; Sep. 15, 1996", Sep. 15, 1997.
Intel Corporation, "Audio Codec '97; Revision 2.0, Sep. 29, 1997", Sep. 29,
1997.
|
Primary Examiner: Hudspeth; David R.
Assistant Examiner: Azad; Abul K.
Attorney, Agent or Firm: Bollman; William H.
Claims
We claim:
1. A device for receiving data from a telephone line in an on-hook
condition, said device comprising:
a scaleable codec having a low power mode capable of operation with only
power drawn from said telephone line in said on-hook condition, and having
a high power mode capable of operation with power drawn from a source
external to said telephone line in an off-hook condition.
2. The device for receiving data from a telephone line in an on-hook
condition according to claim 1, wherein:
said scaleable codec is adapted and arranged to receive call related
information in said on-hook condition.
3. The device for receiving data from a telephone line in an on-hook
condition according to claim 2, wherein:
said call related information is caller ID information.
4. The device for receiving data from a telephone line in an on-hook
condition according to claim 1, wherein said scaleable codec comprises:
an analog-to-digital converter having scaleable order.
5. The device for receiving data from a telephone line in an on-hook
condition according to claim 4, wherein:
said analog-to-digital converter of said codec is adapted and arranged to
operate in a 1.sup.st order in said low power mode.
6. The device for receiving data from a telephone line in an on-hook
condition according to claim 5, wherein:
said analog-to-digital converter of said codec is adapted and arranged to
operate in a 2.sup.nd order in said high power mode.
7. A method of receiving information from a telephone line, said method
comprising:
digitizing in a scaleable codec call related information received from a
telephone line in an on-hook condition using only power drawn from said
telephone line in said on-hook condition; and
converting in said scaleable codec an analog signal received from said
telephone line in an off-hook condition.
8. The method of receiving information from a telephone line according to
claim 7, wherein:
said step of digitizing comprises placing said scaleable codec in a low
power mode; and
said step of converting comprises placing said scaleable codec in a high
power mode.
9. The method of receiving information from a telephone line according to
claim 8, wherein said step of converting further comprises:
providing power from a source external to said telephone line in said
off-hook condition to said scaleable codec.
10. The method of receiving information from a telephone line according to
claim 7, wherein said step of digitizing comprises:
converting said call related information in a first order analog-to-digital
converter in said scaleable codec.
11. The method of receiving information from a telephone line according to
claim 10, wherein said step of converting comprises:
converting said analog signal in a second order analog-to-digital converter
in said scaleable codec, said second order being higher than said first
order.
12. A scaleable codec for receiving information from a telephone line, said
scaleable codec comprising:
means for digitizing call related information received from a telephone
line in an on-hook condition using only power drawn from said telephone
line in said on-hook condition;
means for converting an analog signal received from said telephone line in
an off-hook condition;
said means for digitizing call related information places said scaleable
codec in a low power mode; and
said means for converting comprises placing said scaleable code in a high
power mode.
13. A device for receiving data from a telephone line, said device being
adapted and arranged to be powered from current drawn from said telephone
line in an on-hook state, said device comprising:
a first order sigma-delta analog-to-digital converter, part of a scaleable
codec, adapted and arranged to convert an analog signal into digital
samples;
a regulator to draw power for said scaleable codec from said telephone line
in said on-hook state;
a digital filter to filter said digital samples output from said first
order sigma-delta analog-to-digital converter; and
a frequency shift keying decoder to decode a filtered signal from said
digital filter, and to output decoded data.
14. The device according to claim 13, wherein:
said regulator draws power limited to a first power level during a time
interval corresponding to a reception of said data while said telephone
line is in said on-hook state, and limited to a higher second power level
when said telephone line is in an off-hook state.
15. The device according to claim 14, wherein:
said first power level is about 1.0 mA.
16. The device according to claim 13, wherein:
said digital samples are single bit digital samples.
17. The device according to claim 13, further comprising:
a clock divider to divide a sampling clock to said first order sigma-delta
analog-to-digital converter.
18. The device according to claim 13, further comprising:
a limit/slice module to digitize said filtered signal.
19. The device according to claim 13, further comprising:
a digital amplifier to amplify said analog signal from said telephone line.
20. The device according to claim 13, wherein:
said data corresponds to Caller ID information.
21. The device according to claim 13, wherein:
said first order sigma-delta analog-to-digital converter is adapted to
operate on a line side of said device.
22. A method of receiving data from a telephone line in an on-hook state,
comprising:
digitizing an analog signal from a telephone line using a 1.sup.st order
sigma-delta analog-to-digital converter which is part of a scaleable codec
said scaleable codec using power drawn from said telephone line in said
on-hook state; and
digitally decoding said data from an output of said 1.sup.st order
sigma-delta analog-to-digital converter, using power drawn from said
telephone line in said on-hook state.
23. The method of receiving data from said telephone line in said on-hook
state according to claim 22, further comprising:
digitally filtering said data from said output of said 1.sup.st order
sigma-delta analog-to-digital converter, using power drawn from said
telephone line in said on-hook state.
24. The method of receiving data from said telephone line in said on-hook
state according to claim 22, wherein:
said digitizing produces single bit digital samples of said analog signal.
25. The method of receiving data from said telephone line in said on-hook
state according to claim 22, further comprising:
dividing in half a sampling clock to said 1.sup.st order sigma-delta
analog-to-digital converter.
26. The method of receiving data from said telephone line in said on-hook
state according to claim 22, further comprising:
regulating a voltage drawn from said telephone line in said on-hook state
to provide said power.
27. The method of receiving data from said telephone line in said on-hook
state according to claim 22, further comprising:
digitally amplifying said output of said 1.sup.st order sigma-delta
analog-to-digital converter, using said power drawn from said telephone
line in said on-hook state.
28. The method of receiving data from said telephone line in said on-hook
state according to claim 22, wherein:
said data corresponds to Caller ID information.
29. Apparatus to receive data from a telephone line in an on-hook state,
comprising:
means for digitizing an analog signal from a telephone line using a
1.sup.st order sigma-delta analog-to-digital converter which is part of a
scaleable codec, said means for digitizing being powered by power drawn
from said telephone line in said on-hook state; and
means for digitally decoding said data from an output of said 1.sup.st
order sigma-delta analog-to-digital converter, said means for digitally
decoding said data being powered by power drawn from said telephone line
in said on-hook state.
30. The apparatus to receive data from said telephone line according to
claim 29, wherein:
said means for digitizing is further for outputting single bit digital
samples of said analog signal.
31. The apparatus to receive data from said telephone line according to
claim 29, further comprising:
means for digitally filtering said data from said output of said 1.sup.st
order sigma-delta analog-to-digital converter, said means for digitally
filtering using power drawn from said telephone line in said on-hook
state.
32. The apparatus to receive data from said telephone line according to
claim 29, further comprising:
means for dividing in half a sampling clock to said 1.sup.st order
sigma-delta analog-to-digital converter.
33. The apparatus to receive data from said telephone line according to
claim 29, wherein:
said data corresponds to Caller ID information.
34. The apparatus to receive data from said telephone line according to
claim 29, wherein:
said means for digitizing is adapted to operate on a line side of said
device.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a receiver for information transmitted on a
telephone line. More particularly, it relates to the reception of call
related information, e.g., Caller ID information, on a line side using an
audio codec.
2. Background of Related Art
The reception of call related information before answering an incoming call
is known. For instance, one call related information service is called
Calling Identity Delivery (Caller ID), which is a well known and popular
service provided by many telephone companies. This service provides the
telephone number and household name information of a calling party to the
called party before the call is answered. Based on a display of the Caller
ID information, the called party may decide not to answer the incoming
call. Basic Caller ID information is transmitted from the local telephone
company to the called party while the called party's phone is in a hung-up
or on-hook state, between the first and second rings. Customer premises
equipment capable of receiving Caller ID (CID) information including
Calling Number Delivery (CND) and Calling Name Delivery (CNAM) when the
customer premises equipment is on-hook is generally referred to as Type 1
customer premises equipment.
Waveform (a) of FIG. 6 depicts the signal on a telephone line including
Caller ID information transmitted from a central office to customer
premises equipment. As depicted, the Caller ID information is transmitted
to the customer premises equipment as marks and spaces between a first and
second ring signal. Waveform (b) of FIG. 6 shows the approximate current
draw allowed by customer premises equipment from a telephone line while
the customer premises equipment is on-hook or hung-up, according to
current standards in the United States. Although the customer premises
equipment is permitted to draw additional power from the telephone line
approximately during and between the first and second ring signals while
the customer premises equipment is on-hook, even this additional power is
extremely limited both in amplitude and in duration. Moreover, although
customer premises equipment is permitted to draw significantly more power
while in an off-hook condition, Type 1 Caller ID information is received
entirely while the customer premises equipment is on-hook. Because of the
limited amount of current available from the telephone line while the
customer premises equipment is in an on-hook state, most devices which
receive Caller ID information are either powered by an external power
source, or are generally non-linear analog circuits.
Conventional circuits exist for receiving call related information on a
line side of a telephone circuit. For instance, FIG. 7 shows a
conventional analog circuit for receiving call related information, e.g.,
Caller ID.
In FIG. 7, call related information is coupled through capacitors 702, 704
and transformer T1 even when the on-hook switch 706 is open. Ring signals
are detected by opto-isolator OPTO1. The circuit of FIG. 7 is entirely
analog. Isolation between the high voltage, line side of the circuit (the
right side in FIG. 7) and the low voltage side of the circuit (the left
side in FIG. 7) is provided by transformer T1.
FIG. 8 shows another conventional circuit for receiving call related
information. In FIG. 8, the circuit for receiving the call related
information, e.g., Caller ID, is an analog circuit separated from the main
signal path of the telephone circuit. The call related information signal
path is isolated by isolation capacitors 808, 810, and differentially
input to an operational amplifier (op amp) 820 via resistors 804, 806. The
output of the op amp 820 is input to a codec 830, which digitizes the
signal for processing by the digital signal processor (DSP) 840.
In FIG. 8 the call related information circuit is an analog circuit with
the codec 830 being on the low voltage side of isolation capacitors 808,
810. The codec 830 is powered by an external source in the conventional
circuit of FIG. 8. Moreover, ring signals may be detected either by the
opto-isolator 708 or through the call related information signal path.
Call related information receiving circuits such as those shown in FIGS. 7
and 8 require extra circuits or require that an audio codec, e.g., 730
(FIG. 7) and 830 (FIG. 8), be in a powered-on condition which is wasteful.
For example, a call related information device may be battery or line
powered, relocated easily from place to place, and installed in any
convenient telephone jack. For convenience purposes it may be desirable to
not provide the call related information device with an external power
source. Thus, in these type situations, extra circuits or audio codecs may
be wasteful of available battery or line power.
Similarly, FIG. 9 shows yet another conventional circuit for receiving call
related information that requires extra circuits. In FIG. 9, the circuit
for receiving call related information is a digital circuit separated from
the main signal path of the telephone circuit.
In particular, as shown in FIG. 9, a tip signal T and a ring signal R from
a telephone line are input to a filter 918 and an analog amplifier 916,
which amplifies the analog signal including the call related information
from the telephone line. The output of the analog amplifier 916 is input
to a limit/slice circuit 914, which forms a digital signal for processing
by the OOK modulator 912. The OOK modulator 912 provides on-off keying at
the FSK rate to pass the call related information to the DSP 940 through
isolation capacitors 902, 904. The DSP 940 includes an FSK decode module
to decode the call related information and output the call related
information, e.g., Caller ID data including CND and CNAM, for storage in
log memory and/or for display.
In FIG. 9, the codec 930 remains on the low voltage side of the telephone
circuit, i.e., isolated from the telephone line, in this case by isolation
capacitors 902, 904 and transformer T1. The codec 930 is powered by an
external source, and is not in the path of reception of call related
information. Ring signals may be detected either by the opto-isolator 708
or through the call related information signal path, but in either case
amplitude information with respect to the ring signal is not detected.
There is a need for low power elements allowing processing in a digital
call related information signal path on a high voltage side of a telephone
circuit.
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention, a line-powered
device receives data from a telephone line in an on-hook state. The device
includes a line-powered 1.sup.st order or other very low power codec
sigma-delta analog-to-digital converter which digitizes an analog signal
from the telephone line to digital samples. A digital filter filters the
digital samples output from the first order sigma-delta analog-to-digital
converter, and a line-powered frequency shift keying decoder decodes a
filtered signal from the filtered digital signal, and outputs decoded
data.
A method is also disclosed for receiving data from a telephone line in an
on-hook state. An analog signal from a telephone line is digitized using a
line-powered 1.sup.st order sigma-delta analog-to-digital converter. The
data is digitally decoded from an output of the 1.sup.st order sigma-delta
analog-to-digital converter, and decoded data is provided.
BRIEF DESCRIPTION OF THE DRAWINGS
Features and advantages of the present invention will become apparent to
those skilled in the art from the following description with reference to
the drawings, in which:
FIG. 1 shows a telephone circuit including a low power digital call related
information signal path combined with a main signal path on the high
voltage side of a telephone circuit in accordance with the principles of
the present invention.
FIG. 2 depicts a selectable 1.sup.st or 2.sup.nd order .SIGMA./.DELTA. A/D
converter in an audio codec of the telephone circuit shown in FIG. 1.
FIG. 3 shows the effective circuit of the first order .SIGMA./.DELTA. A/D
converter of the audio codec shown in FIG. 2.
FIG. 4 shows another embodiment of the present invention including a
1.sup.st order .SIGMA./.DELTA. A/D converter utilizing a clock divider to
digitally convert the analog signal including the call related information
at half the sampling rate of the higher order 2.sup.nd order
.SIGMA./.DELTA. A/D converter.
FIG. 5 shows the relevant portions of DSP of FIG. 1 in more detail.
FIG. 6 is a timing diagram showing a conventional signal on a telephone
line including Caller ID information transmitted to customer premises
equipment between first and second ring signals, and of the approximate
maximum allowed current usage by the receiving customer premises equipment
in the United States during the interval between about the first and
second ring signals.
FIG. 7 is a conventional telephone circuit including a combined main signal
path together with a signal path for call related information.
FIG. 8 is another conventional telephone circuit including separate analog
signal paths, i.e., a main signal path and a call related information
signal path.
FIG. 9 is yet another conventional telephone circuit including a digital
call related information signal path separate from an analog main signal
path.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
The present invention provides an audio codec capable of operation on the
high voltage, line side of a telephone circuit, i.e., before the isolation
circuitry. Placement of an audio codec, capable of digitally processing
and demodulating call related information, on the line side improves the
reception of call related information, e.g., Caller ID, reduces costs over
conventional circuitry, and allows reception of call related information
using line power.
A codec (short for COder-DECoder) is an integrated circuit or other
electronic device which combines the circuits needed to convert analog
signals to and from Pulse Code Modulation (PCM) digital signals. Early
codecs converted analog signals at an 8 KHz rate into 8-bit PCM for use in
telephony. More recently, the efficiency and low cost advantages of codecs
have been expanded to convert analog signals at a 48 KHz sampling rate
into 16-bit stereo (and even up to 20-bit stereo) for higher quality use
beyond that required for telephony. With higher quality audio capability,
today's codecs find practical application in consumer stereo equipment
including personal computers (PCs), CD players, modems and digital
speakers.
Improved signal-to-noise (S/N) ratios have been achieved largely by
separating the conventional codec into two individual sub-systems and/or
two separate integrated circuits (ICs): a controller sub-system handling
primarily the digital interface to a host processor, and an analog
sub-system handling primarily the interface to, mixing and conversion of
analog signals. This split digital/analog architecture has been documented
as the "Audio Codec '97 Component Specification", Revision 1.03, Sep. 15,
1996, most recently revised in "Audio Codec '97", Revision 2.0, Intel
Corporation, Sep. 29, 1997 (collectively referred to herein as "the AC '97
specification"). The embodiments disclosed herein include audio codecs
which conform to the AC '97 specification. The documents comprising the AC
'97 specification in their entirety are expressly incorporated herein by
reference.
FIG. 1 shows relevant portions of an audio codec 104 placed on the line
side in accordance with the principles of the present invention. The
inventive audio codec 104 is a delta-sigma (.SIGMA./.DELTA.) audio codec
having scaleable order, e.g., in an analog-to-digital (A/D) converter, to
allow operation in a reduced power mode, e.g., for operation using power
drawn from the telephone line.
In FIG. 1, a tip signal T and a ring signal R are each input to a polarity
guard circuit, which provides a tip polarity signal TP and a ring polarity
signal RP to the audio codec 104. An on-hook switch 706 indicates an
on-hook condition when open. A resistor 140 (e.g., 4.7 megaohms) placed
across the on-hook switch 706 provides current draw on the telephone line
even when the customer premises equipment including the scaleable audio
codec 104 is in an off hook condition, i.e., when switch 706 is closed. A
capacitively coupled event signal comprising the tip signal T is input to
an event detector and transmitter 125 inside the scaleable audio codec 104
for detection of signal activity on the telephone line. The scaleable
audio codec 104 is placed into one of a plurality of power modes depending
upon the on-hook/off-hook condition of the customer premises equipment
and/or whether the customer premises equipment is receiving a ring signal
or call related information, e.g., Caller ID information.
The output of the scaleable audio codec 104 is presented to a digital
signal processor (DSP) 110 for processing and output of the call related
information, e.g., Caller ID information to a display. For off-hook
operation, a digital signal from the DSP 110 is input to a
digital-to-analog converter 124 in the scaleable audio codec 104. The DSP
110 is isolated from the line side by isolation capacitors 106, 108.
The audio codec 104 in the disclosed embodiment is capable of three reduced
power modes which reduce power requirements and allow operation within the
acceptable limits of applicable regulatory requirements. For instance, in
one reduced power mode, the customer premises equipment is in an on-hook
condition with no activity on the telephone line. In another reduced power
mode using slightly more power the event detector and transmitter 125
senses signaling activity on the telephone line. In the first or both of
these reduced power modes the scaleable .SIGMA./.DELTA. A/D converter 140
may be unpowered. In a third reduced power mode, the presence of call
related information is detected by event detector and transmitter 125,
which upon detection initiates a power-up sequence in the .SIGMA./.DELTA.
A/D converter 140 into a 1.sup.st order mode through the system control
module 132.
In normal operation in an off-hook condition, the .SIGMA./.DELTA. A/D
converter 140 is powered up in a higher order mode, e.g., a 2.sup.nd order
mode, which typically requires that external power be drawn. The 2.sup.nd
order mode is a more typical mode of operation of the .SIGMA./.DELTA. A/D
converter 140, and relates to normal operation mode of the .SIGMA./.DELTA.
A/D converter 140 wherein an audio signal such as from a CD player or from
a conversation on a telephone are digitized. Operation of the A/D
converter 140 in the 1.sup.st order mode, while decreasing signal-to-noise
(S/N) ratio performance, provides low and undesirable performance for
digitization of audio signals, but decreases significantly the power
requirements of the scaleable audio codec 104 for non-audio signal
applications such as for the reception of call related information.
In the disclosed embodiment, the scaleable .SIGMA./.DELTA. A/D converter
140 is operable in either a 1.sup.st order mode for detection of call
related information, or in a 2.sup.nd order mode for normal, high power
operation in an off-hook condition. While providing a lowered S/N ratio,
it is found that 1.sup.st order operation is nevertheless sufficient to
receive call related information, e.g., Caller ID information, with
digital processing on a line side. Thus, the scaleable audio codec 104 can
receive call related information, e.g., Caller ID information, or a ring
signal, while being powered by the telephone line.
The scaleable audio codec 104 further includes a main shunt regulator 128
for normal operation, i.e., when in an off-hook condition, which is shut
off in a reduced or low power mode of operation of the scaleable audio
codec 104. A low power shunt 126 receives power from power from a resistor
142. The scaleable audio codec 104 includes a differential to single-ended
converter from the D/A converter 124 to a transistor Q1 to modulate the
telephone line with a signal from the DSP 110 in normal operation, i.e.,
when not in an on-hook condition. The transistor Q1, differential to
single-ended converter module 122, the differential feedback with separate
AC and DC gain module 120, the D/A converter 124 and the main shunt
regulator 128 are unpowered in a reduced power mode of the audio codec. An
event detector and transmitter 125 detects reception of call related
information and/or a ring signal on the telephone line when the scaleable
audio codec 104 is in a low power mode and the customer premises equipment
is in an on-hook condition. A sense resistor Rsense provides signals on
the telephone line to the scaleable .SIGMA./.DELTA. A/D converter 140
through a differential feedback circuit 120 having separate AC and DC
gain. A multiplexer (MUX) 130 outputs to the DSP 110 either the digitized
signals from the scaleable .SIGMA./.DELTA. A/D converter 140, or the event
detector and transmitter 125, based upon selection by a system control
module 132. Possible signals from the event detector and transmitter 125
include a signal corresponding to a ring signal.
In accordance with the principles of the present invention, the scaleable
audio codec 104 is operable in multiple power modes, e.g., a normal, high
power mode wherein full capabilities of an audio codec are available, and
other low power modes wherein the scaleable audio codec 104 can be powered
by current drawn from the telephone line.
In accordance with local telephone standards, the amount of current which
the shunt regulator may draw is typically limited. For instance, as shown
in waveform (b) of FIG. 6, an on-hook device may draw no more than, e.g.,
about 1 microamp (.mu.A) of current based on current U.S. standards,
except for during the time about between the first and second ring signals
of an incoming call, at which time the on-hook device may draw more
current, but no more than, e.g., about 1 milliamp (mA) based on current
U.S. standards. It is important to note that while these current limits
relate approximately to current U.S. telephone standards, any limits
placed on power usage are anticipated and appropriate to the principles of
the present invention. For instance, the present invention is equally
applicable to any appropriate current limits, whether established based on
standards for the country in which the customer premises equipment is
used, or even no current limit at all.
Shunt regulators and other circuits for providing power to customer
premises equipment from a telephone line are known. However, conventional
audio codecs typically require current in excess of that allowable or
desired to be drawn from a telephone line in an on-hook state. The
embodiments of the present invention add selectable order to a
.SIGMA./.DELTA. A/D converter in an audio codec to allow, e.g., reception
of call related information processing, while being powered by a limited
amount of current from a telephone line, i.e., within established limits.
Second and higher order .SIGMA./.DELTA. A/D converter devices are
conventionally preferred in audio codecs, particularly those which conform
largely to the AC '97 specification, to provide the higher S/N ratios
required by the AC '97 specification. Thus, conventional audio codecs do
not generally include a .SIGMA./.DELTA. A/D converter capable of 1.sup.st
order operation as does an audio codec in conformance with the principles
of the present invention.
FIGS. 2 and 3 show the scaleable 2.sup.nd order .SIGMA./.DELTA. A/D
converter 140 (FIG. 1) in more detail.
In FIG. 2, the scaleable 1.sup.st or 2.sup.nd order .SIGMA./.DELTA. A/D
converter 140 includes a first stage 251 and a second stage 252. The first
stage 251 includes a summation element 210 and an integrator 212. The
output of the first stage 251 is input to the second stage 252, which
includes a summation element 214, an integrator 216, and a comparator 218.
The output of the comparator 218 is fed back to both summing nodes 210,
214. The sampling rate of the scaleable 2.sup.nd order .SIGMA./.DELTA. A/D
converter 140 is based on the frequency of a sampling clock input to
comparator 218.
The effective circuit of the scaleable .SIGMA./.DELTA. A/D converter 140 in
the 1.sup.st order mode is shown in FIG. 3. In FIG. 3, signals present on
the tip and ring polarity signals TP, RP are converted into digital
signals by a 1.sup.st order .SIGMA./.DELTA. A/D converter formed by one
stage 252a.
Second order .SIGMA./.DELTA. A/D converters are known. The present
invention modifies an otherwise conventional audio codec such as those
conforming to the AC '97 specification to include a scaleable
.SIGMA./.DELTA. A/D converter 140 which comprises one stage, e.g., the
second stage 252 of an otherwise conventional 2.sup.nd order
.SIGMA./.DELTA. A/D converter. This reduces the scaleable .SIGMA./.DELTA.
A/D converter to be a 1.sup.st order .SIGMA./.DELTA. A/D converter, and
most importantly significantly reduces the power consumed by the audio
codec including the scaleable .SIGMA./.DELTA. A/D converter 140 while the
customer premises equipment is in an on-hook state.
Although the use of a 1.sup.st order of a scaleable .SIGMA./.DELTA. A/D
converter decreases the S/N ratio of the digitized signal output from the
1.sup.st order .SIGMA./.DELTA. A/D converter, the resulting lowered S/N
ratio is still nevertheless adequate to receive and decode the Caller ID
information using digital signal processing. The use of a 1.sup.st order
.SIGMA./.DELTA. A/D converter reduces power consumption of the audio codec
104 while in an on-hook state, allowing isolation of the necessary
portions of the audio codec 104, e.g., the .SIGMA./.DELTA. 1.sup.st order
AND converter 140, to be powered up and receive Caller ID information
while the customer premises equipment is in an on-hook state.
Thus, an audio codec 104 in accordance with the principles of the present
invention includes a 1.sup.st order .SIGMA./.DELTA. A/D converter to
receive and digitize the signal on the telephone line into single bit
.SIGMA./.DELTA. samples.
FIG. 4 shows relevant portions of a second embodiment of the present
invention wherein the power consumption of a line-powered audio codec is
further reduced. In FIG. 4, the scaleable audio codec 104 further includes
a clock divider 260. The clock divider 260 divides the sampling clock by
two. The comparator 218a of a 1.sup.st order .SIGMA./.DELTA. A/D converter
252b in accordance with the second embodiment of the present invention is
then sampled at half the sampling rate as compared to that used by the
comparator 218 of the first embodiment. The slower sampling rate of the
1.sup.st order .SIGMA./.DELTA. A/D converter 252b in the second embodiment
adds substantially to a further decrease in the resulting S/N ratio, e.g.
reduces it from about 85 decibels (dB) to about 30 dB, but nevertheless
still provides a S/N ratio which is more than adequate for the accurate
reception and digital processing of Caller ID information.
Other divisions other than two may be utilized in accordance with the
principles of the present invention. Moreover, slower clocks may be
generated from crystals or other sources, and not necessarily divided from
a higher frequency clock, to provide the slower clock to the comparator
218a shown in FIG. 4.
Although U.S. standards allow as much as 1 mA of current to be drawn during
the reception of Caller ID information, the present invention provides a
scaleable audio codec 104 which can receive and decode Caller ID
information using about 0.3 to 0.4 mA of current. When the scaleable audio
codec 104 is performing functions other than receiving and demodulating
Caller ID information, e.g., when providing the basis for a modem, it is
powered either by the telephone line or from an external source.
Instead of a single A/D converter having two orders of operation, a
separate 1.sup.st order A/D converter may be provided to receive the call
related information. In this case, the separate 1.sup.st order A/D
converter is configured as shown in FIG. 3.
The scaleable audio codec 104 is in communication with a digital signal
processor (DSP) 110 to perform digitally the substantial equivalent of the
call related information signal path of the conventional circuit shown in
FIG. 9.
In particular, as shown in FIG. 5, the DSP 110 receives the digital
.SIGMA./.DELTA. encoded signal output from scaleable .SIGMA./.DELTA. A/D
converter 140. The DSP 110 then digitally amplifies the signal if
necessary in amplifier module 110a. The amplified signal is digitally
filtered in digital filter 110b to isolate the call related information,
e.g., the Caller ID information from the signal on the telephone line. The
signal output from the digital filter 110b is input to a limit/slice
module 110c, which limits and slices the filtered signal into portions for
use by an FSK decoder 110d. The FSK decoder 110d decodes data in the
signal and outputs the received call related information. The digital
processes of amplification, filtering, limit/slicing and FSK decoding
implemented in DSP 110 are well known in the art.
While the invention has been described with reference to the exemplary
embodiments thereof, those skilled in the art will be able to make various
modifications to the described embodiments of the invention without
departing from the true spirit and scope of the invention.
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